As some said, you do not want to use it the same way as other lenses. For this, when used indoors, do not use AF-C as it will hunt.

On Pany bodies (the OP has a G3), the lens is not even allowed to enter AF-C as far as I know. My G1 doesn't allow it and I think later Pany bodies behave similarly.

I used it first on a GH1. I do not recall if it can be used in the AF-C mode for still, but in video mode, it will do AF-C by default.

Yes, I was referring to stills only when I said the body wouldn't allow it.

Just had a look. On the G3 AFC is greyed out.

Yes, that's what I thought.

Video AF is somewhat painful indeed.

IIRC, it's not just the noise. It's also slow in video (IIRC, I only tried once), perhaps because they are afraid that the mechanism might overheat if it's running fast and continuously. That may also be part of the reason why Pany bodies won't allow it to use AF-C for stills.

Is this lens unique in this? I will check all my other lenses...

As I recall (but I am not sure), it is unusually slow in video compared to other lenses. It is surely unique in that it Pany bodies do not allow it use AF-C for stills.

So should use MF in video. I almost exclusively MF in video anyway but the video targeted lenses (such as the power zooms) do AF quite well in video if someone wants to use that feature. So it's a minus for the 20 in that respect.

I hardly shoot any video. But if I did, I'd probably try to MF too. The back-and-forth search that CDAF has to perform looks pretty bad (disturbing) to me in video. PDAF (which should be useable with video if it's on the sensor) should be able to do better in that regard but I have no idea whether it is at all used for video on the only MFT cam that has it (E-M1).

The problem if you try to MF during video with native MFT lenses is that they are no good for pulling focus with precision due to their focus-by-wire design (except possibly those Oly lenses that have the special MF focus clutch). Even with focus by wire, a given distance on the focus ring should correspond to a given change in focus. But that's not the case. It depends not only on how far but also how fast you turn the ring. Completely idiotic in my not so humble opinion.

A bit like flicking on an iPad, do you want precision movements or some kind of interpretation of your speed/acceleration added in to enhance your gestures? They chose to enhance it with the derivatives which is not unreasonable as if you focus slowly you are into precision and if you move fast you want to travel a long distance. They of course should have added the capability of distance only without any derivatives for video, but in the absence of that, they did provide shooting without a lens

I am afraid no excuses are good enough in this case.

However I quickly learned not to do that so even in video, I use only AF-S. I also use the lens on E-PL5 but I never bother to find out whether it works in AF-C, which is to be avoided with this lens.

Right. No point moving to AF-C even when the body allows it (as does my E-M5).

Agree. Probably has changed with the E-M1's PD?

I'll believe it when/if I see it. My E-M1 should arrive any day now. But it does not seem all that clear if/how the E-M1 uses PDAF for AF-C with native MFT (as opposed to FT) lenses. And to the extent that it does, it remains to be seen if that helps any with the 20. I am not holding breath and honestly don't care much. The lens is already doing perfectly well for what I want to use it for.

The last sentence sounds like famous last words. When you discover a new capability and start using it, you will look back and find it hard to image how you could have tolerated life without it. I used to think that standard issue sliced white bread was all I needed for bread. Now I can only vaguely recall those dark ages

As you know, I am hardly among those who speak against the blessings of technical innovation. It's just that I have so far never found any reason to use this lens with AF-C or in ways where its AF-S behavior is really bothersome.